This invention relates to energy absorbers. More particularly it relates to seismic isolation bearings able to provide isolation from and to absorb energy imparted by outside forces of a wide range of magnitudes.
Lead rubber bearings and rubber bearings known in the art are described in WO 94/13974; U.S. Pat. No. 4,177,637; U.S. Pat. No. 4,499,694; U.S. Pat. No. 4,593,502; and U.S. Pat. No. 4,713,917. Such bearings have been primarily used in seismic isolation of structures. Seismic isolation involves increasing the natural period of a structure to outside the period of the exciting motion. This reduces the forces transmitted into a structure through decoupling. The addition of an improved damping mechanism to dissipate the associated energy, thereby controlling the displacements and further reducing the accelerations transmitted to a structure establishes a seismic protection system.
Bearings used in the seismic isolation of structures to date have each been designed to absorb external forces of a narrow range of magnitudes. It would be desirable to have a bearing with the ability to absorb forces of a wide range of magnitudes to provide both isolation for small displacements and good damping for large displacements.
It is an object of this invention to go some way towards achieving this desideratum or at least to offer the public a useful choice.
Accordingly, the invention may be said broadly to consist in an energy absorbing bearing comprising:
a pair of end plates,
a substantially integral laminate comprising alternating layers of resilient material and stiffening members interposed between said end plates,
each said end plate being connected to said laminate at or adjacent to a central axis running from one end plate through said laminate to the other end plate, but not otherwise,
the unconnected adjacent surface portions of said laminate being capable of limited movement relative to each said end plate when said bearing is being acted upon by an external force.
In one embodiment there is provided an insert of plastically deformable material along said central axis extending substantially from one said end plate to the other side end plate.
In another embodiment said laminate is continuous from side to side and end to end without an insert.
In another alternative there is an empty core along said central axis extending substantially from one said plate to the other said plate.
In another alternative there are provided a plurality of inserts within said laminate.
Preferably said bearing has a regular cross-section.
In one embodiment the cross-section of said end plates and laminate is square.
In another embodiment the cross-section of said end plates and laminate is circular.
Preferably the cross-section of said insert is circular.
Alternatively the cross-section of said insert is square.
Preferably said stiffening members comprise rigid plates.
Preferably said rigid plates are of plastically deformable material.
More preferably said rigid plates have some elasticity as well as being of plastically deformable material.
Preferably, when said insert is present, it is compressed at a hydrostatic pressure at least approaching the shear yield stress of said plastically deformable material.
Preferably said insert material is lead.
Alternatively said insert material is high purity aluminum, tin, zinc, indium or iron, or alloys of lead, aluminium, tin, zinc, indium or iron or any superplastic alloy or other material having a low rate of work hardening.
In still a further alternative said insert material is densely packed granular material such as is described in U.S. Pat. No. 4,713,917.
In one embodiment said granular material is steel, glass beads, alumina, silicon carbide or any other similar hard granular material.
Alternatively said granular material is granular iron, lead, aluminium or other similar less hard material.
Alternatively said insert has a square cross-section.
Alternatively said insert is of variable geometric cross-section.
Preferably said insert has an hour glass shape when viewed in side elevation.
Preferably said insert has a regular geometric cross-section.
Preferably said resilient material is rubber.
Preferably said end plates are made of steel.
Alternatively said end plates are made of aluminium or aluminium alloy.
Alternatively said end plates are of ceramic material, fibreglass or other suitable material.
Preferably said end plates are adapted to have some flexibility in the direction along said central axis.
Preferably said laminate has steel plates as stiffening members, there being provided fixing means for fixing each stiffening plate at an end of said laminate to its adjacent end plate. Preferably a said insert is present in said bearing and each said fixing means abuts an end of said insert.
In another embodiment the invention is a method of isolating a structure from seismic forces acting upon it which comprises:
providing a seismic isolating bearing having a pair of end plates and a laminate of alternating layers of elastomer and stiffening material between said end plates, the end plates being secured to the top and bottom of said laminate only in the area adjacent a central axis passing through said end plates and said laminate, resting said structure on one said end plate and resting the other said end plate on the ground or another structure, and
where necessary, securing said structure to one said end plate and securing the other said end plate to the ground or to another structure.
Preferably said seismic isolating bearing is as defined above.
In another embodiment the invention may be said broadly to consist in a laminate for use between a pair of end plates in a seismic isolating bearing comprising:
an outer laminate zone having alternating layers of elastomer and stiffening members, the planes of each said layer being, in use, substantially parallel to each other and to said pair of end plates,
a bore extending substantially through said laminate having a central axis orthogonal to the planes of said layers,
an inner laminate zone within said bore also having alternating layers of elastomer and stiffening members, the planes of each of which being, in use, substantially parallel to each other and to said pair of end plates,
said inner laminate zone itself having a central core of plastically deformable material,
said stiffening members of said inner zone extending sufficiently far outwardly to overlap with the inward edges of the stiffening members of said outer zone.
Preferably said laminate has a regular geometric cross-section.
In one embodiment said laminate is substantially circular.
In another embodiment said inner zone is circular and said outer zone is square.
Preferably said stiffening members are rigid plates.
Preferably said elastomer is rubber.
Preferably said laminate has means in/or adjacent to said inner laminate zone for attaching said end plates to said laminate.
In another embodiment the invention may be said broadly to consist in a laminate for use between a pair of end plates in a seismic isolating bearing comprising:
an outer laminate zone having alternating layers of elastomer and stiffening members, the planes of each said layer being, in use, substantially parallel to each other and to said pair of end plates,
a bore extending substantially through said laminate having a central axis orthogonal to the planes of said layers,
an inner laminate zone within said bore also having alternating layers of elastomer and stiffening members, the planes of each of which being, in use, substantially parallel to each other and to said pair of end plates,
said inner laminate zone itself having a central core of plastically deformable material,
said laminate having means in or adjacent to said inner laminate zone for attaching said end plates to said laminate.
Preferably said laminate has a regular geometric cross-section.
In one embodiment said laminate is substantially circular.
In another embodiment said inner zone is circular and said outer zone is square.
Preferably said stiffening members are rigid plates.
Preferably said elastomer is rubber.
In one embodiment said stiffening members extend outwardly from said core of plastically deformable material but stop short of the boundary between said inner and said outer laminate zones.
In another embodiment the invention may be said broadly to consist in the combination of a pair of end plates with a laminate immediately described herein above.
Preferably in said combination said end plates are attached to said laminate in the vicinity of the centres of said end plates and said inner laminate zone.
In another embodiment the invention may be said broadly to consist in a connector for making a once only connection between two members comprising:
a male connector member having a cylindrical end portion with a substantially flat end face, an annular recess in said end portion adjacent to said end face and a channel open at its radial side and axial end having a radial depth substantially the same as the radial depth of said recess and a width along its radial side at least as wide as the width in an axial direction of said annular recess extending substantially spirally from said end face into said annular recess, and
a female connector member having a plate like portion of thickness to fit within said annular recess, a circular bore through said plate like portion with a diameter slightly greater than the diameter of the bottom of said axial recess in said first connector member,
a guiding member in said female connector member comprising a portion of the outer periphery of said circular bore cut radially outwardly and bent axially away from a cross-sectional plane of said bore at an angle substantially the same as that of the spiral path of said channel in said male connector member, whereby
when said flat end of said cylindrical portion of said male connector member is pressed against the periphery of said bore of said female connector member with said guiding member directed into said channel of said male connector member and said male connector member is rotated while still being pressed against said female connector member, said guiding member rides up said channel into said axial recess and is straightened thereby and is followed by the remainder of the periphery of said bore so that, after one complete revolution of said male connector member, said connector members are permanently joined with the periphery of said bore being within said annular recess.
Preferably said male connector member is a threadless bolt which is suitable for passing through a bore through the centre of an end plate in an energy absorbing bearing as hereindefined and said female connector member is a stiffening member in a laminate in a said bearing closest to an end plate.
In another embodiment said male member has two said channels into said recess which are open at their radial sides and axial ends and said female member has two said guiding members, said channel axial ends and said guiding members being in registry with one another when said male member is placed against said female member.
In a still further embodiment there are three or more said channels in said male member and a corresponding number of guiding members in said female member.
Preferably when there is more than one said channel in said guiding member each channel is symmetrically disposed about its respective male and female members.
In a still further embodiment the invention may be said broadly to consist in an energy absorbing bearing comprising:
top and bottom end plates,
a substantially integral laminate comprising alternating layers of resilient material and stiffening members interposed between said plates,
said bottom end plate being connected to said laminate at or adjacent to a central axis running from one said end plate through said laminate to the other said plate but not otherwise,
said top end plate not being secured to said laminate but constrained by guiding means from moving horizontally relative to said laminate while being capable of reciprocal vertical movement relative to said laminate,
the unconnected adjacent surface portions of said laminate being capable of limited movement relative to each said end plate when said bearing is being acted upon by an external force.
In one alternative said guiding means comprises an upright pin secured in said laminate and projecting upwardly beyond the thickness of said upper plate and a bore through said upper plate, the pin fitting loosely in said bore so that said upper plate can move reciprocally vertically relative to said laminate.
In another alternative said pin is secured to said upper plate projecting downwardly and the loosely fitting bore is in said laminate.
This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
The invention consists in the foregoing and also envisages constructions of which the following gives examples.